FIG. 1 shows the basic structure of a drive train of a motor vehicle known from the prior art, which has an auxiliary output on the engine side. Thus, the drive train in FIG. 1 comprises a drive aggregate consisting of an internal combustion engine 1, with a transmission 3 connected between the internal combustion engine 1 and a drive output 2. The transmission 3 converts rotational speeds and torques and thereby transmits traction force provided by the internal combustion engine 1 to the drive output 2. In the drive train of FIG. 1, a clutch 4 is connected between the internal combustion engine 1 and the transmission 3, by means of which the internal combustion engine 1 can be decoupled from or coupled to the drive output 2, and which in particular serves as a transmission-external starting element. As an alternative, a transmission-internal starting element can also be provided.
In addition the drive train of FIG. 1 has an auxiliary output 5 on the engine side, which in the example shown is formed by a cooling aggregate 6 and a refrigerating trailer 7 which is cooled by the cooling aggregate 6. The auxiliary output 5 on the engine side, also called an engine-side PTO (Power Take Off), is coupled to the internal combustion engine 1 by a continuously variable transmission 8 and a generator 9 in such manner that when the internal combustion engine 1 is running, the continuously variable transmission 8 provides substantially constant rotational speed at the drive input of the generator 9 regardless of the actual speed of the internal combustion engine 1, so that regardless of the actual speed of the internal combustion engine 1 the generator can deliver a defined electric input for operating the auxiliary output 5. In this case the continuously variable transmission 8 is a hydraulic continuously variable transmission. However, the continuously variable transmission 8 can also be in the form of a mechanical continuously variable transmission or an electric continuously variable transmission, for example comprising two electric machines and two rectifiers.
In particular, regardless of the actual running speed of the internal combustion engine 1 the generator 9 delivers a defined electric alternating voltage characterized by a defined voltage potential and a defined voltage frequency for operating the auxiliary output 5.
According to the prior art, to operate such a drive train with an engine-side auxiliary output 5, the procedure is to regulate a condition parameter of the engine-side auxiliary output 5, the latter having a storage function in relation to the condition parameter, by means of a regulator associated with the engine-side auxiliary output 5. In FIG. 2, as the condition parameter for the engine-side auxiliary output 5 comprising the cooling aggregate 6 and the refrigerating trailer 7, a temperature T inside the refrigerating trailer 7 is shown, which can be regulated by a regulator of the cooling aggregate 6 between two limit values TMIN and TMAX in such manner that the temperature in the refrigerating trailer 7, which varies with time t, ranges between these limit values.
For this purpose, according to the prior art a two-point regulator is used as the regulator of the cooling aggregate 6. Such a two-point regulator exclusively compares whether the current actual value of the condition parameter, i.e. in FIG. 2 the actual temperature, is between the limit values and, depending on the result of the comparison, the auxiliary output 5, namely in the example embodiment of FIG. 1 the cooling aggregate 6, either draws energy or power from the internal combustion engine 1, or not.
From the standpoint of energy such operation of the drive train is not favorable. In particular, it can lead to higher fuel consumption by the internal combustion engine. A method is therefore needed for operating a drive train having an auxiliary output on the engine side, by virtue of which fuel consumption can be reduced.